In an integrated circuit memory device (e.g., silicon-based), a polycrystalline silicon is used as a preferred material for forming a gate pedestal in field effect transistors (FETs). As long as the integrated circuit memory device is relatively large (e.g., where a critical dimension of the integrated circuit memory device greater than 0.5 microns), additional circuit lines (e.g., a gate line) may be made using the polycrystalline silicon (e.g., in a layer) used for forming the gate pedestal. However, when the integrated circuit memory device shrinks, resistance of the gate pedestal based on the polycrystalline silicon alone may be too high.
In order to lower the resistance (e.g., without the additional circuit lines), a transition metal (e.g., nickel, cobalt) may be deposited on top of source/drain silicon or the gate pedestal made of the polycrystalline silicon and/or annealed to form a silicide. The silicide is a compound of the transition metal and the source/drain silicon or the polycrystalline silicon of the gate. However, a photo mask needed to form the silicide may not be viable when the integrated circuit memory device is scaled.
Alternatively, a self-aligned silicide (e.g., salicide) may be used to lower the resistance in the integrated circuit memory device as the salicide does not require a lithographic patterning process. In a typical salicide process, the transition metal may be deposited over the FETs formed on a wafer. Then, the wafer is heated to allow the transition metal to react with silicon in active regions (e.g., sources, drains, and/or gates) of the wafer. Once the salicide process is completed, any remaining transition metal may be removed by chemical etching.
For the salicide to be effective in lowering the resistance, the compound being formed (e.g., as the product of the salicide) has to be thick (e.g., hundreds angstroms). However, the thick salicide may cause a defect in junction areas and lead to high junction leakage and malfunction of the IC. For example, roughness of the thick salicide may short the junction. A deeper junction may be used to accommodate the thick salicide, but the deeper junction increases the dimension of the junction area, thus resulting in increase in the die size.